Packoff subassembly

ABSTRACT

A packoff subassembly comprises the body having a first camming member secured at one end thereof and a second camming member supported thereon for relative sliding movement with respect thereto. The first and second camming members have outwardly angularly extending camming surfaces facing one another, and an elastomeric seal is mounted between the camming surfaces. A hub extends from the end of the body remote from the first camming member and threadedly receives a nut adapted to move the first and second camming surfaces toward one another thereby forcing the elastomeric seal outwardly and into sealing engagement with the surrounding surface.

TECHNICAL FIELD

[0001] This present invention generally to down hole tools of the type utilized in conjunction with hydrocarbon wells and the like, and more particularly to a packoff subassembly useful in conjunction with perforating guns.

BACKGROUND & SUMMARY OF THE INVENTION

[0002] In the construction of hydrocarbon wells and the like, a borehole is formed in the earth. Casing is extended into the borehole and the space between the casing and the borehole is filled with cement. The function of the casing and the cement is to isolate the various strata penetrated by the borehole thereby preventing the escape of valuable hydrocarbons, preventing ground water contamination, etc.

[0003] In order to recover hydrocarbons through the borehole it is necessary to perforate the sections of the casing and the cement which are aligned with producing strata. Frequently, a perforating gun is used for this purpose. A perforating gun comprises a length of pipe which contains explosive charges designed to perforate the casing and the cement comprising the well in which the perforating gun is used. In order for a perforating gun to function properly, the ends thereof must be sealed in order that the contents of the pipe are not contaminated by liquids, etc.

[0004] The sealing technique which is presently utilized in conjunction with perforating guns comprises machining each end of the pipe section comprising the perforating gun to provide interior threaded sections and smooth sealing sections at each end of the pipe. Sealing members comprise threaded portions which threadedly engage the threaded sections of the pipe and O-ring seals which engage the sealing sections located at the opposite ends of the pipe. Threaded engagement of the threaded portions of the sealing members with the threaded sections of the pipe retain the sealing members in place, and engagement of the O-ring seals of the sealing members with the sealing sections at the pipe ends prevent contaminants from entering the pipe and thereby interfering with the operation of the perforating gun.

[0005] The difficulty with the foregoing sealing technique for perforating guns comprises the fact that upon operation of the perforating gun, dirt and other debris becomes lodged in the threaded connection between the pipe ends and the sealing members. This phenomenon renders removal of the sealing members from the ends of the pipe comprising the perforating gun difficult to the extent that additional personnel must be employed to remove the sealing members from the pipe ends and to clean and otherwise restore the threaded sections within the ends of the pipe and threaded portions of the sealing members to facilitate reuse. In some instances the contamination of the threaded connections between the perforating gun pipe and the sealing members is so severe that the sealing members are damaged or destroyed during removal thereof.

[0006] The present invention comprises a packoff subassembly which overcomes the foregoing and other problems which have long since characterized the prior art. In accordance with the invention the necessity of providing threaded sections and sealing sections at the opposite ends of a perforating gun pipe is eliminated.

[0007] A packoff subassembly for use in conjunction with perforating gun pipes comprises a cylindrical body having a threaded end. A first camming member is threadedly engaged with the threaded end of the body and extends to a first camming surface. A second camming member is supported on the body for relative sliding movement therebetween and comprises a second camming surface which faces the camming surface of the first camming member. An elastomeric seal is positioned between the camming members and is provided with end surfaces which engage the facing camming surfaces thereof.

[0008] The upper end of the second camming member is provided with a radially extending shoulder. A hub is secured on the end of the body remote from the threaded end thereof and is provided with a threaded section adjacent the intersection between the body and the hub. A nut is threadedly engaged with the threaded portion of the hub and is aligned with the shoulder of the second camming member such that upon rotation of the nut relative to the hub the first camming member is drawn toward the second camming member thereby causing the camming surfaces of the camming members to force the elastomeric seal outwardly.

[0009] In the practice of the invention the above-described packoff subassembly is inserted into the cleaned but unmachined end of a perforating gun pipe. The nut on the hub is employed to draw the first camming member toward the second camming member thereby expanding the elastomeric seal into engagement with the interior of the pipe. This action continues until a sufficient seal has been formed between the sealing member and the pipe. The packoff subassembly of the present invention is adapted to seal the interior of a perforating gun pipe against contamination by liquids, etc. even though the pipe is out of round, contaminated by scale and other debris, etc.

[0010] After the perforating gun has been fired, the nut is rotated in the opposite direction relative to the hub. This action allows the first sealing member to move away from the second sealing member thereby allowing the elastomeric seal to return to its original configuration. At this point the packoff subassembly is easily removed from the end of the perforating gun pipe and is ready for reuse.

[0011] In actual practice it has been found that use of the present invention results in substantial savings both in eliminating the costs involved in machining the opposite ends of the perforating gun pipe and in reducing the number of personnel which are needed to install and remove the seals utilized to prevent contaminants from entering the perforating gun.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A more complete understanding of the invention may be had by reference of the following Detailed Description when taken in conjunction with the accompanying Drawings, wherein:

[0013]FIG. 1 is a sectional view illustrating the packoff subassembly of the present invention; and

[0014]FIG. 2 is a sectional view illustrating the use of the packoff subassembly of the present invention in conjunction with a perforating gun.

DETAILED DESCRIPTION

[0015] Referring now to the Drawings, and particularly to FIG. 1 thereof, there is shown a packoff subassembly 10 comprising the present invention. The packoff subassembly 10 includes a cylindrical body 12 which extends to a threaded end 14. A first camming member 16 is secured to the body 12 by threaded engagement with the threaded end 14 thereof. The first camming member 16 has a first camming surface 18.

[0016] A second camming member 20 is slidably supported on the body 12 for relative sliding movement with respect thereto. The second camming member 20 is provided with four threaded apertures 22 positioned at 90° intervals around the circumference thereof. The second camming member 20 further comprises a second camming surface 24 which faces the camming surface 18 of the first camming member 16. The second camming member 20 extends to a shoulder 26 positioned at the end thereof remote from the camming surface 24.

[0017] As will be apparent from FIG. 1, the first camming surface 18 of the first camming member 16 extends angularly outwardly from the body 12 and toward the second camming member 20. The second camming surface 24 of the second camming member 20 extends angularly outwardly from the body 12 and toward the first camming member 16. In accordance with other embodiments of the invention, the first and second camming surfaces 18 and 24 can extend radially, that is, non-angularly, from the body 12.

[0018] A hub 28 is secured to the body 12 of the packoff subassembly 10. The hub 28 is provided with threaded sections 30 and 32 situated at the end thereof remote from the threaded section 14 of the body 12. The hub 28 further comprises a threaded section 34 having a nut 36 threadedly engaged therewith.

[0019] The packoff subassembly 10 further comprises an elastomeric seal 38. The seal 38 comprises a sealing surface 40 extending substantially parallel to the longitudinal axis 42 of the packoff subassembly 10. The elastomeric seal 40 further comprises an angularly extending surface 44 which engages the surface 18 of the first camming member 16 and an angularly extending surface 46 which engages the surface 24 of the second camming member 20.

[0020] As will therefore be understood by those skilled in the art, rotation of the nut 36 relative to the hub 28 causes the nut 36 to engage the shoulder 26 of the second camming member 20. Further rotation of the nut 36 relative to the hub 28 draws the first camming member 16 toward the second camming member 20. Because the first camming member 16 is fixedly engaged with the body 12, movement of the first member 16 towards the second camming member 20 compresses the elastomeric seal 38 therebetween, thereby forcing the sealing surface 40 outwardly into engagement with a surrounding surface. In certain applications of the invention, a washer 48 may be disposed within the interior of the elastomeric seal 38 to present inward collapse thereof.

[0021] In the practice of the invention the first camming member 16, the elastomeric seal 38 (in its uncompressed configuration) and the second camming member 20 comprise right circular cylinders which are substantially equal to diameter to the inside diameter of a pipe section in which the packoff subassembly 10 will be employed. The shoulder 26 of the second camming member 20 engages the end of the pipe section to position the packoff subassembly 10 with respect thereto. Apertures are formed in the pipe section in alignment with the apertures 22 formed in the second camming member of the packoff subassembly 10. Threaded fasteners are extended through the apertures in the pipe section and into the threaded apertures 22 to secure the packoff subassembly within the pipe section. The threaded fasteners do not extend into the threaded apertures 22 sufficiently to engage the body 12, and therefore do not interfere with relative sliding movement between the body 12 and the second camming member 20.

[0022] The packoff subassembly 10 may also be provided with a passageway 50 extending axially therethrough along the axis 42. The purpose of the passageway 50 is to direct the electrical leads necessary for the operation of a perforating gun into the interior of a pipe section comprising the perforating gun.

[0023] Referring now to FIG. 2, there is shown a perforating gun 56 comprising a pipe section 58 having packoff subassemblies 60 and 62 incorporating the present invention installed on the opposite ends thereof. The packoff subassembly 60 is identical in construction and function to the packoff subassembly 10 illustrated in FIG. 1 and described hereinabove in conjunction therewith.

[0024] The packoff subassembly 62 is similar to the packoff subassembly 10 but differs therefrom in that it is not provided with threaded sections at the end thereof similar to the threaded sections 30 and 32 of the packoff subassembly 10. The packoff subassembly 62 further differs from the packoff subassembly 10 in that it does not have a passageway extending axially therethrough such as the passageway 50 of the packoff subassembly 10.

[0025] In the practice of the invention the pipe section 58 is cut to length and is deburred. The interior portions of the pipe section 58 adjacent the ends thereof are brushed to remove dust and debris but do not require machining. Four apertures 64 are formed in each end of the pipe section 58 at 90° intervals around the periphery thereof.

[0026] The packoff subassembly 62 is positioned in the end of the pipe section 58 that will become the upper end of the perforating gun 56. The packoff subassembly 62 is positioned in the end of the pipe section 58 will become the lower end of the perforating gun 56. Threaded fasteners are inserted through the apertures 64 of the packoff subassembly 60 and 62 and are threaded engaged with threaded apertures performed in the second camming members of the packoff subassemblies 60 and 62 and identical in construction and function to the threaded apertures 22 of the packoff subassembly 10. The threaded fasteners do not extend into the threaded apertures of the second camming members of the packoff subassemblies 60 and 62 sufficiently to prevent relative sliding motion between the second camming members and the bodies of the packoff subassembly 60 and 62.

[0027] The threaded fasteners function to secure the packoff subassemblies 60 and 62 to the pipe section 58. After installation of the threaded fasteners has been completed, the nuts on the hubs of the packoff subassemblies 60 and 62 corresponding to the nut 36 of the packoff subassembly 10 of FIG. 1 are rotated relative to the hubs thereof. This action draws the first camming members of the packoff subassemblies 60 and 62 towards the second camming members thereof thereby compressing the sealing members of the packoff subassemblies and forcing the sealing surfaces thereof into engagement with the interior of the pipe section 58. This action continues until a sufficient seal between the packoff subassemblies 60 and 62 and the pipe section 58 has been formed. In actual practice it has been found that packoff subassemblies incorporating the present invention are capable of forming seals which exceed the bursting strength of the pipe sections in which they are installed.

[0028] After the packoff subassemblies 60 and 62 have been installed in the pipe section 58, the perforating gun 56 is lowered into a well and is operated. Following operation thereof, the perforating gun is removed from the well. At this point the nuts of the packoff subassemblies 60 and 62 are rotated to disengage the seals between the packoff subassemblies and the pipe section 58, and the threaded fasteners which secure the packoff subassemblies within the pipe section 58 are removed. The packoff subassemblies 60 and 62 are then removed from the pipe section 58 and are ready for reuse in another perforating gun.

[0029] Although preferred embodiments of the invention as illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions of parts and elements without departing from the spirit of the invention. 

1. A packoff subassembly comprising: a body having a first camming surface extending outwardly therefrom; a second camming surface supported on the body for movement toward and away from the first camming surface; an elastomeric seal supported on the body between the first camming surface and the second camming surface; and means for selectively moving the first camming surface and the second camming surface toward one another and thereby forcing the elastomeric seal outwardly from the body and into sealing engagement with the surrounding surface.
 2. The packoff subassembly according to claim 1 wherein the first and second camming surfaces face one another, and wherein the elastomeric seal comprises opposed surfaces engaging the first and second camming surfaces.
 3. The packoff subassembly according to claim 1 further including: a first camming member secured to the body and having the first camming surface formed thereon; and a second camming member supported on the body and having the second camming surface formed thereon; and the second camming member and the body being supported for relative sliding movement with respect to each other.
 4. The packoff subassembly according to claim 3 wherein the first camming surface extends toward the second camming member and angularly outwardly relative to the body, and wherein the second camming surface extends toward the first camming member and angularly outwardly relative to the body.
 5. The packoff subassembly according to claim 4 further characterized by a threaded member for effecting relative movement between the body and the second camming member.
 6. A packoff subassembly comprising: a cylindrical body; a first camming member fixedly secured to one end of the cylindrical body; a first camming surface formed on the first camming member; a second camming member supported on the body; a second camming surface formed on the second camming member; a second camming member and the body being supported for relative sliding movement with respect to each other; the first camming surface and the second camming surfacing facing one another; an elastomeric seal supported on the cylindrical body between the first camming surface and the second camming surface; and means for effecting relative sliding movement between the second camming member and the body in a direction that moves the first camming surface and the second camming surface toward one another thereby forcing the elastomeric seal outwardly and into engagement with a surrounding surface.
 7. The packoff subassembly according to claim 6 wherein the first camming surface extends angularly outwardly from the body and toward the second camming member; the second camming surface extends angularly outwardly from the body and toward the first camming member; and the elastomeric seal comprises surfaces mounted in engagement with the first and second camming surfaces.
 8. The packoff subassembly according to claim 7 wherein the first camming member is cylindrical in shape and is characterized by a predetermined diameter; the second camming member is cylindrical in shape and is characterized by a predetermined diameter substantially identical to the diameter of the first camming member; and the elastomeric seal is cylindrical in shape and is characterized by an initial diameter which is substantially identical to the diameters of the first camming member and the second camming member.
 9. The packoff subassembly according to claim 8 further including a hub extending from the end of the body remote from the first camming member and comprising a threaded section located immediately adjacent the intersection of the hub and the body; and a nut threadedly engaged with the hub for selectively effecting relative sliding movement between the second camming member and the body.
 10. The packoff subassembly according to claim 9 further including a plurality of threaded apertures formed in the second camming member for securing the packoff subassembly in engagement with an end of a length of pipe. 